1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly to a LCD module and a LCD device that can minimize the movement of a light guide plate received in a mold frame by improving the structure of the light guide plate and the mold frame of the LCD device.
2. Description of the Related Art
Recently, an information processing device has been developed to have various shapes, various functions, and a rapid information processing speed. The information processed in the information processing device has an electrical signal. In order to confirm the information processed in the information processing device with the naked eye, a display device that functions as an interface device is needed.
Recently, a LCD device that is lighter, and smaller than a CRT type display device has been developed. The LCD device now displays a full color spectrum in a high resolution. As a result, the LCD device is widely used as a computer monitor, a television receiver, and other display devices.
The LCD device applies a voltage to a liquid crystal layer to change the molecular arrangement of the liquid crystal layer. The LCD device changes the optical properties in the liquid crystal and uses the modulation of a light by using a liquid crystal cell.
There are two kinds of LCD devices: a TN (Twisted Nematic) type, and an STN (Super-Twisted Nematic) type. Also, they can be grouped into an active matrix display type that uses a switching device and a TN liquid crystal, and a passive matrix display type that uses a STN liquid crystal according to the driving type.
The active matrix display method is used in a TFT-LCD and drives an LCD by using a thin film transistor (TFT) as a switch. The passive matrix display method does not use any transistor and does not require a complex circuit.
Further, LCD devices are grouped into a transmissive LCD device that uses a backlight and a reflective LCD device that uses an exterior light source, according to a method for using a light source.
The transmissive LCD device using the back light as a light source is relatively heavy and voluminous due to the back light, but it is widely used since it does not use an exterior light source and displays an image independently from the exterior light source.
FIG. 1 is an exploded perspective view schematically showing a conventional LCD device. FIG. 2 is a partial exploded perspective view of the LCD device shown in FIG. 1.
Referring to FIG. 1, the LCD device 900 has a LCD module 700 to which an image signal is applied to display an image, and a front case 810 and a rear case 820 for receiving the LCD module 700.
The LCD module 700 has a display unit 710, which includes a LCD panel for displaying the image.
The display unit 710 has a LCD panel 712, an integrated and printed circuit board 714, a data side tape carrier package 716, and a gate side flexible circuit board 718 manufactured by the COF (chip-on-film) method.
The LCD panel 712 has a TFT substrate 712a, a color filter substrate 712b, and a liquid crystal layer (not shown) interposed therebetween.
The TFT substrate 712a is a transparent glass substrate on which TFTs are formed in a matrix shape. Data lines are connected to source terminals of the TFTs, and gate lines are connected to gate terminals of the TFTs. Pixel electrodes of indium tin oxide (ITO), which is a transparent conductive material, are formed on drain terminals.
If electrical signals are inputted to the data lines and to the gate lines, the electrical signals are inputted to the source terminals and to the gate terminals of TFTs and the TFTs are turned on or off so that electrical signals for forming pixels are outputted to the drain terminals.
The color filter substrate 712b is attached to the TFT substrate 712a. RGB pixels that pass light through to realize color display are formed on the color filter substrate 712b by a thin film process. A common electrode comprised of ITO is coated on the front surface of the color filter board 712b. 
If electric power is applied to the gate terminals and to the source terminals of the transistors and the TFTs are turned on, an electric field is formed between the pixel electrode on the TFT substrate and the common electrode of the color filter substrate. The arrangement angles of the liquid crystals injected between the TFT substrate 712a and the color filter substrate 714b are changed by the electric field, and the light passages are changed due to the arrangement angle changes to obtain a desired pixel status.
A driving signal and a timing signal are applied to the gate line and to the data line of the TFT to control the arrangement of the liquid crystal of the LCD panel 712 and the timing when the liquid crystal is arranged. The data side tape carrier package 716, which is a kind of flexible circuit board for determining the timing when the data driving signal is applied, is attached to the source side of the LCD panel 712, and the gate side flexible circuit board 718 manufactured by the COF method for determining the time when the gate driving signal is applied is attached to the gate side of the LCD panel 712.
The integrated and printed circuit board 714 for receiving image signals from outside of the LCD panel 712, and for applying driving signal to the gate line and to the data line, is connected to the data tape carrier package 716 of the data line side of the LCD panel 712. The integrated printed circuit board 714 has a source portion to which the image signals generated from an exterior information processing device (not shown), such as a computer, are applied to provide the data driving signals to the LCD panel 712 and a gate portion for providing the gate driving signals to the gate line of the LCD panel 712. Namely, the integrated printed circuit board 714 generates the gate driving signals for driving the LCD device, the data signals, and a plurality of timing signals for applying the signals. The gate signals are applied to the gate line of the LCD panel 712 through the gate side flexible circuit board 718, and the data signals are applied to the data line of the LCD panel 712 through the data tape carrier package 716.
A back light assembly 720 for providing a uniform light to the display unit 710 is provided under the display unit 710. The back light assembly 720 has a lamp 721, which is provided on one side of the LCD module 700 to generate the light. The lamp 721 is protected by a lamp cover 722. A light guide plate 724 has a size corresponding to the LCD panel 712 of the display unit 710, and is located under the LCD panel 712. The lamp side of the light guide plate 724 is thicker than the other side opposite to the lamp side, and it guides the light generated by the lamp 721 towards the display unit 710 to change the passage of the light.
A plurality of optical sheets 726, for making the luminance of the light irradiated from the light guide plate 724 and passed towards the LCD panel 712 uniform, are provided above the light guide plate 724. A reflection plate 728, for reflecting the light leaked from the light guide plate 724 to increase the efficiency, is provided under the light guide plate 724.
The display unit 710 and the back light assembly 720 are fixed and supported by a mold frame 730 that is a receiving receptacle. The mold frame 730 has a box-shape, and the upper surface of the mold frame 730 is open. That is, the mold frame 730 has four side walls and a bottom surface, and openings, for bending the integrated printed circuit board 714 along the outer side surface of the mold frame 730 and positioning the integrated printed circuit board 714, are formed on the lower surface of the bottom.
A chassis 740 for bending the integrated printed circuit board 714 of the display unit 710 and the gate tape carrier package 718 outside of the mold frame 730, and for fixing the integrated printed circuit board 714 of the display unit 710 and the gate tape carrier package 718 to the bottom surface of the mold frame 730 to prevent the deviation of the display unit 710, is provided. The chassis 740 has a box-shape in the same manner as a mold frame 730. The upper surface of the chassis 740 is opened to expose the LCD panel 710, and the side walls are bent inwardly to cover the upper surface peripheral portion of the LCD panel 710.
On the other hand, referring to FIG. 2, first and second catching bosses 731 and 732 are integrally formed with the mold frame 730 on the corner portions of the mold frame on which the lamp 721 (see FIG. 1) is installed in the receiving space of the mold frame 730. The corner of an end portion, which is located on the side of the lamp 721 in the light guide plate 724 received in the mold frame 730, is cut off to form first and second catching jaws 724a and 724b. 
FIG. 3 shows the state in which the light guide plate shown in FIG. 2 is received in the mold frame. FIG. 4 is a partially enlarged view of section “P1” showing the fixing structure of the light guide plate shown in FIG. 3 and the mold frame. FIG. 5 is a top view showing the size of the light guide plate shown in FIG. 3.
Referring first to FIG. 3, if the light guide plate 724 is received in the mold frame 730, the first and second catching jaws 724a and 724b are engaged with the first and second catching bosses 731 and 732. Therefore, even when exterior impacts are applied to the LCD device 900, the light guide plate 724 does not move towards the lamp 721 due to the presence of first and second catching bosses 731 and 732.
However, it is now desirable for the thickness of the side wall of the mold frame 730 to become thinner so as to minimize the size of the LCD device 900. Further, as shown in FIG. 5, the width of the light guide plate 724 of the end portion of the side of the lamp 721 is identical to the width of the end portion of the opposite end portion. That is, width W1 equals width W2. Therefore, it is not easy to sufficiently guarantee the thickness of the first and second catching bosses 731 and 732 that are integrally formed with the mold frame 730. Therefore, as shown in FIG. 4, the catching force of the first and second catching jaws 724a and 724b of the light guide plate 724 and the first and second catching bosses 731 and 732 of the mold frame 730 can not be sufficiently guaranteed so that preventing the light guide plate 724 from moving towards the lamp 721 is difficult.
On the other hand, if the width of the light guide plate 724 increases by the gap between the light guide plate 724 and the mold frame 730 to guarantee the catching force (i.e., by width W3), the catching force of the first and second catching jaws 724a and 724b and the first and second catching bosses 731 and 732 can be obtained. However, without the gap between the light guide plate 724 and the mold frame 730, the thermal expansion space of the light guide plate 724 according to the temperature change and the humidity change cannot be guaranteed, thereby greatly inducing the folding phenomenon. Especially, in the wedge type light guide plate 724 shown in FIGS. 1 and 2, since the thermal expansion rate is large at the portion where the light guide plate 724 is thin, the sufficient gap between the light guide plate 724 and the mold frame 730 is necessary.
On the other hand, even though it is not shown in the figure, the movement of the light guide plate 724 can be prevented by protruding a portion of both side surfaces of the light guide plate 724, forming a boss, and forming a recess at a position that corresponds to the boss on both side walls of the mold frame 730. However, in that case, it is not easy to guarantee the catching force between the boss and the recess and to prevent the light inputted from the lamp 721 from being concentrated at a corner portion defined by the boss and the recess.